This invention relates to computer image generation (CIG) and, more particularly, to a method for spatial augmentation of vertices with continuous level of detail transition for obtaining continuous smooth transformation between effective levels of polygon density, in part by creating new vertices in response to predetermined data descriptors.
Typically, objects to be displayed in a scene of a computer image generation (CIG) system are represented by edges of polygons, or faces, the vertex descriptors of which are stored in a data base. Some form of transition between different levels of detail (LODs) for representing objects to be displayed in CIG systems is also generally used. The use of different LODs enable objects that are more distant from a viewpoint to be represented by fewer polygons, thereby requiring fewer polygon edges to be processed and conserving computing resources for closer objects which typically require more detail and correspondingly more edges in order to be accurately and realistically represented. Transitions between LODs occur at respective predetermined ranges, or zones or regions, from a viewpoint with each lower, or more distant LOD, having correspondingly fewer edges assigned to corresponding features and therefore less detail for objects to be displayed.
In early CIG systems, transition from one LOD to another LOD occurred at respective predetermined ranges from a viewpoint and would be abrupt when the predetermined range was reached. Inasmuch as the human perception system is very sensitive to abrupt transition, this effect during image presentation was distracting and detracted from the goal of achieving realism.
The development of translucent face capability for CIG systems made possible a significant improvement in implementation of transitions between LODs. For example, in a system for generating an image of viewable terrain (i.e. features--both of natural nature, such as land, water, and the like, and of artificial nature, such as roads, structures and the like-- of some environment, such as a location on or in the Earth, Space, the Sea, other planets, etc.), an LOD transition translucency control factor applicable to each LOD at the transition zone between adjacent LODs, and that monotonically increases from 0 to 1 (0 percent to 100 percent) at a predetermined rate in response to the change in range as an observer moves toward a scene can be used to control the translucency of faces from adjacent LODs. The translucency control factor determines the translucency of a face, from opaque at 0 to transparent at 1 with proportionate fractional values of translucency in between. At the proximate boundary of the transition zone the fine terrain faces of the lower detail LOD are opaque (control factor=0) and the fine terrain faces of the higher detail LOD are transparent (control factor=1). Continuing across the transition zone, a point is reached at which the coarse LOD faces have a translucency of x, say 25%, and the fine LOD faces have a translucency of (1-x), say 75%. In progressing through the transition zone, some point will be reached at which the coarse and fine LOD faces each have a translucency of 50%. At the remote boundary of the transition zone the fine LOD faces will be transparent and the coarse LOD faces will be opaque.
Although translucency blending during LOD transition is an improvement over abrupt switching of LOD information, there are still cases where translucency blending does not provide accurate and/or unambiguous results. For instance, if the fine LOD contains a peak of terrain that extends above the terrain of the coarse LOD and a feature, such as a vehicle, is spatially defined to be behind the peak of fine terrain, then at the 50--50 percent of translucency transition, the scene will show the feature as a blend of 50% feature definition (faces) and 50% terrain definition (faces), thus making the feature appear to be in front of the terrain even though spatially it was defined to be behind the terrain. This effect is known as bleedthrough.
In another example, it is sometimes requires to determine when a collision between objectives occurs. If, for example a vehicle is represented by faces with one percent translucency and a feature that is a potential target for a collision is represented by 99 percent translucency, then although the feature will not be visible to the observer, a collision between the vehicle and the feature will be detected.
Other potential deficiencies include inability to provide a face from either one LOD or the other that validly represents vehicle position and attitude at all points in the transition zone between LODs, and inefficiency in computer processing because all faces in the transition zone from both LODs must be processed to determine proper assignment of subpixel color and texture modulation for ultimate display.
It would be desirable to provide a method for overcoming position, attitude and collision ambiguities, bleedthrough effects, subpixel processing inefficiencies caused by having multiple polygon groups (one from each adjacent LOD) representing a single object, and other deficiencies that may be associated with prior CIG systems during LOD transitions. In addition it would be desirable to achieve smooth and continuous LOD transition without resort to translucency blending.
Accordingly, it is an object of the present invention to provide a method for smooth and continuous LOD transition for eliminating position, attitude and collision ambiguities, bleedthrough effects, subpixel processing inefficiencies caused by having multiple polygon groups representing a single object, and other deficiencies that may be associated with prior CIG systems caused by LOD transitions during image presentation.
Another object of the present invention is to provide a method for creating desired finer detail from predefined coarser data for effective continuous smooth LOD transitions.
Yet another object of the present invention is to provide a method for achieving smooth and continuous LOD transition without resort to translucency blending.
Still another object of the present invention is to provide a method for achieving smooth LOD transition by generating finer detail that is available from predefined data without having to predefine and/or store most of the finer detail.